1. Field of the Invention:
This invention relates to systems for transporting and sorting articles and in particular to automated systems for transporting and sorting articles, including parcels and sacks of mail.
2. Description of the Prior Art:
Automated systems for transporting and sorting articles, such as parcels, envelopes and other postal articles, are known in the art. Such systems typically include a conveyor mechanism, such as, for example, a conveyor belt or a series of closely spaced rollers, for propelling the articles and a series of secondary tracks or chutes down which selected articles are diverted according to their respective destinations. A control system, which typically includes an optoelectric sensor for detecting the movement of the articles on the conveyor track, is provided for controlling the operation of the conveyor track and selectively activating individual ones of a plurality of diverter mechanisms located along the main conveyor track. Examples of such automated conveyor systems are shown in U.S. Pat. Nos. 2,609,928; 3,580,391; 3,651,936; 3,955,678; and 4,432,458.
Typically, at a bulk mail center where packages, which are referred to in the trade as "non-machineable outsides" or "NMO's", and sacks containing small packages and envelopes are placed on metal trays, which are attached to and transported by a continuous conveyor chain or belt. The destination of each article is entered into the control system and when an article reaches a predetermined position along the conveyor track, the metal tray tilts and the article slides down a chute into a bin corresponding to its destination. The decision to tilt a particular tray with an article down a specific chute is determined indirectly by a method known as "shaft encoding". Shaft encoding involves counting the number of revolutions made by the conveyor chain drive shaft and correlating this number to a distance traveled by the metal tray along its path. The metal trays are tilted when the appropriate number of revolutions are made that corresponds with the destination chute for the article on the tray. This type of control system requires the continual adjusting of the relationship of the shaft revolutions to the chute positions due to changes in chain length (slack), tilt response time, other mechanical wear, and signal pickup reliability. An additional problem associated with this type of conveyor mechanism is that the metal trays are not well-suited for NMO's and very large sacks and it is often difficult to properly position the NMO's and sacks at the center of the trays, which often results in instability of the articles and premature tipping of the trays if the article is loaded off-center.
Another type of conveyor system used in bulk mail centers operated by the U.S. Postal Service for NMO's is comprised of a main track of closely spaced apart rollers on which the articles are initially loaded and a plurality of secondary tracks intersecting the main track at selected locations therealong, to which selected articles are diverted. A computer-implemented control system keeps track of the relative positions of the articles on the main track and selectively operates an air cylinder which shifts a set of rollers at the intersection of the main track and the selected secondary track to divert the article to that secondary track. Because the rollers must have substantial spacing therebetween to allow the rollers to shift sufficiently to divert an article, this type of conveyor system is not suitable for transporting sacks of mail, particularly partially filled sacks of mail, which are referred to in the trade as "skins", and other articles of irregular shape, because of the likelihood of portions of such articles becoming trapped in the spacings between the individual rollers. Thus, a conveyor system is not available in the prior art which is suitable for conveying and sorting NMO's and sacks of mail of various sizes and shapes.